1. Field of the Invention
The present invention relates generally to sound damping coating compositions.
2. Background Information
Automotive OEM have used precut asphalt- or rubber-based patches as liners for floor pans, deck lids and doors of automobiles in order to dampen and/or reduce road and/or engine noise and vibrations thereby preventing these sounds from permeating into the passenger compartment of the motor vehicle. Sprayable coating compositions, which are capable of being applied by robotics, are desirable for a number of reasons. For example, these coating compositions typically provide labor, reduced part inventories, flexibility in design specifications for damping properties as well as other cost savings over their asphalt/rubber based counterparts. At times, waterborne or high solids coating compositions are used in applications where only air dry cure is feasible.
Traditionally, when an aqueous based sound damping coating composition is applied onto a substrate and allowed to dry, the evaporation of water from the coating composition during automotive bake conditions can result in defects in the dried coating. As used herein, “defects” means the pita defects or pita gaps that can occur in a coating as it dries. In general, pita can be described as an area in the coating layer where the coating layer has separated thereby leaving an air pocket. In some instances, the length of the pita gap can extend more than 13 mm when measured along a plane that is substantially parallel to the surface of the substrate when a coating layer having the approximate dimensions of 75 mm (L)×75 mm (W)×2 mm (T) is applied onto the substrate. In other instances, the length of the pita gap can extend approximately 75% of the coating layer described in the preceding sentence. It will also be noted that these defects can occur not only near the surface of the coating layer, but in the bulk region of the coating layer as well as near the interface between the coating layer and the substrate.